Systems are commercially available that permit an operator to edit or modify the color and composition of an original image to form a more aesthetically pleasing reproduction of the image in hard copy form. One example of such a system is the KODAK PREMIER Image Enhancement System manufactured by the Eastman Kodak Company of Rochester, N.Y. The KODAK PREMIER Image Enhancement System incorporates a film reader unit to digitally scan original images in the form of negatives, transparencies or lithographic film and display the scanned original images at an operator workstation which includes a monitor, keyboard, and digitizing tablet, with accompanying stylus, coupled to a processing unit. An operator can utilize the workstation to alter the original images by cropping, rotating, resizing, changing the color balance, or performing a multitude of other manipulation functions. The altered original images are then reproduced in hard copy form by a writing unit.
In addition to the features listed above, it is also desirable to incorporate an interactive electronic "airbrush" manipulation function within the system, i.e., a function that permits the operator to retouch the original image displayed in video form on the monitor of the workstation in a manner similar to conventional airbrushing of photographic negatives or prints. The operator can use the airbrush function to lighten, darken, change the contrast, or add color to selected areas of the displayed image. U.S. Pat. No. 5,276,510 entitled "Airbrush Modeling Routine for an Electric Image Reproduction System", for example, discloses an airbrush modeling routine that closely models the operation of a conventional airbrush in both function and result.
It has been found that conventional electronic image reproduction systems are not adequate for use in producing a variety of common image enhancement effects such as shadows, glows, highlights and vignettes. The best an operator can presently hope to accomplish is to use an airbrush function as described above in an attempt to manually create a reasonably smooth gradation in an image. Even the most experienced users, however, find it very difficult to create smooth, natural contours and gradients manually.
In view of the above, it is an object of the invention to provide an electronic image reproduction apparatus that is capable of producing smooth and natural contours and gradients required to create common enhancement effects such as shadows, glows, highlights and vignettes.